Current Sensor and Method for Motor Control

Abstract

The present invention provides an improved motor current sensor and methods thereof. A first embodiment of the present invention provides a circuit having a signal transfer unit for receiving first and second input signals from opposing terminals of a shunt resistor and a signal conditioner unit for conditioning output signals from the signal transfer unit for a low power control unit. A second embodiment of the present invention provides a circuit having a signal conditioner unit for receiving first and second input signals from opposing terminals of a shunt resistor and delivering output signals to a signal transfer unit and finally to a level shifter for providing first and second voltage signals to a control unit.

Description

BACKGROUND OF THE INVENTION [0001]1. Field of the Invention[0002]The present invention relates generally to the field of current sensors and methods for motor control. More specifically, the present invention relates to an improved current sensor and current sensor components for motor control.[0003]2. Background of the Prior Art[0004]In the field of motor control circuitry, there is always a system performance related issue of how to get motor phase current information accurately and instantly to the motor control unit.[0005]The motor control unit is generally a low power circuitry configuration comprising a digital signal processor and / or microcontroller. In contrast, the motor phase currents are generated by a high voltage switching mode power supply. Such voltages are too high to be connected directly to the motor control unit, otherwise such voltages would cause damage to the low power circuitry of the motor control unit. As a result, various current sensors have been developed...

AI Technical Summary

Benefits of technology

[0025]The present invention provides an improved current sensor and method for motor control. In a first embodiment of the present invention a current sensor comprises a signal transfer unit for receiving a first and a second high voltage signal as inputs and providing a corresponding first and second low voltage signal as output corresponding to a difference between the high voltage inputs. The high voltage signals are received from opposing terminals of a shunt resistor, wherein the shunt resistor is connected to a first and second high voltage switch component at one terminal and to the motor at the opposite terminal.

[0026]The current sensor further comprises a signal conditioner wherein the low voltage output of the signal transfer unit is received as input. The signal conditioner provides a first output voltage that is in proportion to the current passing through the shunt resistor and a second output that provides a reference voltage. Both outputs from the signal conditioner are within the low voltage range wherein they may be connected to a control unit and the motor current can be measured therefrom by the control unit.

[0027]In an alternative embodiment of the present invention, a current sensor comprises a signal conditioner unit for receiving a first and second high voltage signal as input from a shunt resistor connected to a motor. The signal conditioner provides a first high voltage as an output proportionate to the difference between the first and second high voltage signal inputs, plus an output of a reference voltage.

[0028]The output from the signal conditioner is provided to a signal transfer unit which converts first and second high voltage signals to first and second low voltage signals as outputs. Finally, a voltage level shifter unit receives first and second low voltage signal outputs from the signal transfer unit and shifts first and second signals to a first output voltage that is in proportion to the current passing through the shunt resistor and a second output that provides a reference voltage. Both outputs from the voltage level shifter unit are within the low voltage range wherein they may be connected to a control unit and the motor current can be measured therefrom by the control unit.

Problems solved by technology

In the field of motor control circuitry, there is always a system performance related issue of how to get motor phase current information accurately and instantly to the motor control unit.

Such voltages are too high to be connected directly to the motor control unit, otherwise such voltages would cause damage to the low power circuitry of the motor control unit.

However, switching components 1 and 2 may never be on at the same time.

One disadvantage of this prior art circuit is that the working frequency is limited to maximum of 20 kHz.

Another disadvantage is that it needs an external synchronous signal from control unit 10 that must be at most equal to or lower than switching frequency (20 KHz).

The disadvantages of this prior art system is the complexity and low speed of the current sensor 11.

The overall cost and circuit complexity are thus increased due to more digital interfaces 14 needed for multi channel shunts in multiphase motor control.

Another disadvantage of this prior art circuitry is its resolution / speed trade-off.

These time delays compromise too much performance in, e.g., 20 khz switching frequency motor control.

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